YZF750 shock linkage HELP!!!!!

[yamtastic]

Aye up all!

Just bought this 1994 YZF750R for trackday fun and was giving it the once over in the garage when I saw the spring on the rear shock is touching the frame! Now I'm no genius but I'm pretty sure this aint good!

The shock is the pretend ohlins from an SP version of the YZF and the linkage and dogbones look standard, however somethings amiss if the spring touches the frame!!!

So can anyone shed any light on the matter???

The dogbones are 172mm ish long (centre of bolt hole to same at other end) and have 4BH stamped on them and the linkage has 24FM-00 on it

Any help would be bloody great as this thing needs to be right before venturing out onto track!

[Kayla]

'4FM' is the right model code for the YZF and the dog bones are the right length... Is there anything on the upper mount that's extending the shock's effective length? Some kind of spacer or a stack of washers? Would turning the linkage around make a difference? On all the Yams I've had the longer end of the bell crank goes in the frame. I'm kind of clutching at straws here

[originalracingsnake]

Can the linkage be bolted through the other hole, next to the one it is on? Looks like it is in the wrong hole to me. FNARRR.

[porter_jamie]

is the rocker on the right way around? ie back to front, not upside down, if you see what i mean....

[porter_jamie]

http://www.cmsnl.com/yamaha-yzf750rh-1996_...0404/partslist/

[chrisexup]

As far as i know my 1994 YZF750SP is standard.

The dog bones are approx 180mm long, and they carry the same number that is cast into the linkage, 4FM-10

[alexp5]

Are you sure the shock isn't bent? In this picture it looks like the damper rod has a definite kink in it

That ain't gonna help matters.

[yamtastic]

Hi all

According to the all knowing haynes manual the linkage is in the right way round and after whipping the shock out to check it is straight (however dont scare me like that again! )

The bike is suspended from the garage roof at the minute but looked the same with it on the deck, just wondered if the linkage was off this model or something else possibly which was bringing the shock closer to the frame???

The grind a bit off the lugs on the frame idea had occured but thought I'd take the subtle approach first and see if we could fathom it out!!!

There's nothing else on the shock like washers etc...I know this because its on the list of jobs to do to raise the back a bit! That or thunderace dogbones I hear have a similar effect!

[yamtastic]

PS thanks for the parts list and photo's of the standard set up guys, I appreciate the time This forum is bloody great.

[alexp5]

Must be the dogbones then. Get hold of some standard YZF ones and try 'em out. I wouldn't of thought the shock would foul the frame though, i know with 'Ace dogbones it gets close. Is the shock off an SP? , IIRC they're longer. This + 'ace dogbones would do it.

edit to add: PM Strappy. His YZF has 'Ace dogbones and a Maxton shock. Have a polite word in his shell and ask him to have a look at his rear end (fnarr).

[Kayla]

All different dog bones will do is move the swingarm relative to the frame. The shock and bell crank form a triangle which the dog bones just hang off. Is the spring the correct one (fatter coils maybe?)

[Kayla]

Is the shock off an SP? , IIRC they're longer.

Ahhhh... that'd do it

edit- which explains the different part number on the SP linkage- 4FM-10 must be the SP part and 4FM-00 is the normal part.

[yamtastic]

So! Do I need the SP linkage and dogbones to correct it?

I would like to raise the rear to help steering, would the SP dogbones (180mm) lower it again???

I'm easily confused!!!

[chrisexup]

I would like to raise the rear to help steering, would the SP dogbones (180mm) lower it again???

Yes.

i've got a pair of 165mm tie bars, with 12mm bolt holes if you want to try them at some point....

[yamtastic]

OK!!!

I don't suppose anyone knows where I could get an SP linkage???

[Kayla]

OK!!!

I don't suppose anyone knows where I could get an SP linkage???

It might be easier (and cheaper!) to find an 'R' shock. How long is the SP shock you've got? Just out of curiosity and that.

[alexp5]

OK!!!

I don't suppose anyone knows where I could get an SP linkage???

No, but it might be worth phoning Maxton as I believe they used to do a 'revised rocker linkage' (their blurb... not mine) for an R which mimicked the SP's dimensions. I may be talking pap now as I'm currently destroying brain cells

What have we established..?

You have a 750R with a 750R rocker and dogbones, and mebbe a 750SP shock ?

I wouldn't worry about the rocker for now, try the shorter 'bones (or 'Ace ones) and see if this works.

[Kayla]

I wouldn't worry about the rocker for now, try the shorter 'bones (or 'Ace ones) and see if this works.

It won't. Sorry to be a pain in the bum, but shorter or longer dog bones will only move the swingarm up or down. It seems the (possibly) longer SP shock is (possibly) pushing the standard 'R' bell crank too far around/down, moving the bottom of the shock further in towards the frame which is why the spring is fouling on the frame. The spring needs to be moved away from the frame and only a different bell crank or shorter shock will do that. The bell crank is a fixed length, the unloaded shock is a fixed length and the distance between the top shock mount and the frame/linkage mount is a fixed length- changing the dog bones won't affect this.

[suspensionsmith]

What you could try which is wasy is spin the spring around 180 degrees so the coil is open where it is close too the frame..may give you the clearance you need,

But first raise the rear wheel off the ground and measure from the axle too a point above on the bike,thats how far the rear is extending now,then spin the spring around and measure again to see if the rear has extended.

What you could then do is remove the spring completely and put the shock(damper only) back in and see how far the rear is extending without the interference of the spring.